1. Field of the Invention
The present invention relates to fabrication technology of a semiconductor photoelectronic device, specifically to a fabrication method of GaN power LED with electrodes formed by composite optical coatings.
2. Description of Prior Art
Since white-light LEDs were invented, the application area of high-brightness LEDs has been extended to the market of high-efficiency light source. Compared with prior illumination light sources, the light source using LEDs has the benefits of energy conservation, long life period, small volume, high luminous efficiency, no pollution, having various colors and the like. The energy consumption of a white-light LED is only ⅛ of that of a filament lamp, and only ½ of a fluorescent lamp. The life period of the white-light LED can be up to one hundred thousands hours. Moreover, the white-light LEDs can be made mercury-free, which is very important in view of the demand for environmental protection and energy conservation. As the most commonly-used method of achieving the white-light LEDs, a blue-light chip of InGaN/GaN multi-quantum wells (MQW) is used to excite a yellow-light fluorescent powder (YAG: Ce3+). The semiconductor solid light source has a good prospect of being used as a green solid light source in a new-generation illumination revolution, due to a deep research on the blue-light material of the InGaN/GaN MQW and a steady improvement in the property of the manufactured white-light power LED devices.
Despite the great development in the research on GaN power LEDs, which rapidly increases the illumination efficiency, there is still a long way to achieve the object of completely replacing the conventional light sources. Current problems in quantum efficiency, current distribution uniformity and heat dissipation capacity of the device are technical bottleneck in a further improvement of the property of a LED. How to increase an extraction efficiency of the light emitted from a power GaN LED is one of the most important problems under research.
To solve the problem with respect to the extraction efficiency of the light emitted from a power GaN LED, those skilled in the art have proposed many solutions with respect to device configurations, fabrication processes, or the like, such as a flip-chip structure, a resonant cavity structure, a metal reflector, surface coarsing, using a photonic crystal, or the like, and have made much progress. Especially in a preparation of electrodes, a transparent electrode is often used for a P—GaN electrode. However, for the N—GaN electrode, a metal ohmic contact electrode is usually used, which certainly degrades the extraction efficiency of the LED because the metal has a high absorption coefficient for the light. The present invention proposes a novel design and a novel fabrication method of a GaN-based power LED with P and N electrodes formed by transparent composite optical coatings with high light extraction efficiency.